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A068813 Primes with a 3 followed by 1's. 1
31, 311, 311111, 31111111111, 311111111111, 31111111111111, 31111111111111111111111111111111111, 311111111111111111111111111111111111111111111111, 31111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..9.

Makoto Kamada, Prime numbers of the form 311...11.

H. C. Williams, Some primes with interesting digit patterns, Math. Comp. vol 32 no 144 (1978) pp 1306-1310, Table 2, r=3.

Index entries for primes involving repunits

EXAMPLE

Digit 3 followed by rep-units of length 1,2,5,10,11,13,34,47,52,77,88,...

MATHEMATICA

Select[Table[FromDigits[PadRight[{3}, n, 1]], {n, 2, 100}], PrimeQ] (* Harvey P. Dale, Nov 18 2012 *)

PROG

(PARI) for(n=1, 200, if(isprime(3*10^n+(10^(n)-1)/9)==1, print1(3*10^n+(10^(n)-1)/9, ", ")))

CROSSREFS

Cf. A002275, A056704.

Sequence in context: A200913 A212235 A126552 * A221306 A142382 A137318

Adjacent sequences:  A068810 A068811 A068812 * A068814 A068815 A068816

KEYWORD

nonn,base

AUTHOR

Amarnath Murthy, Mar 07 2002

EXTENSIONS

More terms from Benoit Cloitre, Mar 09 2002

One additional term from Harvey P. Dale, Nov 18 2012

STATUS

approved

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Last modified October 13 16:50 EDT 2019. Contains 327968 sequences. (Running on oeis4.)